1. Field of the Invention
The present invention relates in general to the field of current mirrors used in integrated circuits. More specifically, the present invention provides an improved current mirror that compensates for the effects of current mismatch related to gate leakage in semiconductor devices.
2. Description of the Related Art
A current mirror is a current source that generates an output current that is controlled by an input reference current. Current mirrors are employed in a wide variety of applications where it is necessary to have an accurate, reliable current source. Current mirrors are particularly useful for accurately replicating a reference current source at multiple locations in a circuit.
Many of the advances in size reduction of complimentary metal oxide semiconductor (CMOS) transistors in integrated circuits in recent years have been based on the concept of scaling. The scaling concept is based on the theory that a large CMOS transistor can be “scaled” to produce a smaller CMOS transistor having similar operational characteristics. One of the limitations to the scaling concept, however, relates to the phenomenon of quantum mechanical tunneling of electrons through very thin gate oxide layers. In deep submicron design, gate oxide thickness is scaled essentially to a few layers of silicon atoms. Therefore, direct tunneling currents become significant factors in operation of circuits such as current mirrors. Direct tunneling currents in the CMOS components used to implement a current mirror can become so pronounced that the reference and the mirrored output currents are no longer equal, thereby destroying the benefit of using a current mirror.
Because of the current mismatches that can result in a current mirror due to gate leakage currents in CMOS circuit components, there is a need for an improved current mirror that is capable of compensating for the effects of gate current leakage.